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build a variable phase adjust for sub?

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Damon

How would I go about building a variable phase adjustment for my subwoofer? It only has a phase reversal switch, but I would like to build something that is continuously variable to help with the blend now that my sub is up front between my mains. I know moving the mains would acconplish the same thing but I want to have an adjustment on the sub. Thanks.

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Re: build a variable phase adjust for sub? klaus 01:46:53 01/25/00 (2)
1. Here's a simple phase shift control (constant 1-gain):
http://www.bluesmobil.com/shikhman/info/phaser.gif
Phase shift floats with input F, but you'd only need it for an octave or two.
2. Tweak the filter slope of your sub filter. This blending technique is used in Audiocontrol XO that I use and it works. For a LP filter with Sallen-Key topology, increase feedback C for a sharper slope (more phase delay), decrease it for shallower slope (less delay). For HP channel, tweak feedback R. Actually, you can change other elements too, but the feedback chain affects filter behavior stronger.
- Thanks, Klaus. What opamp do I use? Damon 08:16:21 01/25/00 (1)
  Even though I can't read the language I understand the schematic. What I do not know is what opamp to use. Can you describe its parameters or give me some part numbers? Thank you very much for your help.
  - Re: Thanks, Klaus. What opamp do I use? klaus 08:55:21 01/25/00 (0)
    For the sub channel, amp speed isn't critical, use any low distortion amp.
    On the low-cost side, TI 5534 is ok. I didn't test a lot of other opamps myself and rely on Audio Analogue's designer notes published here:
    http://www.pi.infn.it/~federico/donizetti.htm (bottom of page)
    I used it in a prototype crossover so far so good.
    This amp has pins for DC bias and high-F adjustment. DC needs no adjustment unless there's a very big (megaOhms) ground-to-input resistor. You must add HF adjustment cap (20-40 pF between pins 5 and 8).

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